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Sub clinical and clinical hyperthyroidism?

Could somebody please tell me the difference between sub clinical and clinical hyperthyroidism? I have tried to research but either I can't find a definitive answer or my brain just won't let it in because I still don't really know.

My endo mentioned this on the phone whilst discussing my low TSH due to me taking a higher dose of T3 than prescribed(20mcg). He's allowed me to stay on the higher dose pending a blood test in 6 weeks and after this, wants to put it back down to 10mcg and increase my T4 from 50mcg to 75mcg instead.

I'm in the process of trying to write a letter, with all my unanswered questions, research and arguments to his case but it's taken me a week so far and I just can't concentrate. So if anyone could explain this in basic terms I would be grateful. I realise it has something to with what's showing on blood tests to symptoms or no symptoms but that's about it. lol

Thank you :)

16 Replies

Hi Denise

I looked at your profile but there is no background of your history.

I am not sure whether or not you have been diagnosed with hypothyroidism or hyperthyroidism. So I am guessing you may be hypo, if so this is the only excerpt I can see if someone is hypo and taking thyroid hormones but because the TSH is very low it is referred to:-

This ‘exogenous subclinical hyperthyroidism’ is not dangerous as long as serum T3 is unequivocally normal

This is an extract from an article by Dr Toft and if you want a copy email

6 What is the correct dose of thyroxine and is there any rationale for adding in tri-iodothyronine?

The appropriate dose of levothyroxine is that which restores euthyroidism and serum TSH to the lower part of the reference range – 0.2-0.5mU/l.

In this case, free thyroxine is likely to be in the upper part of its reference range or even slightly elevated – 18-22pmol/l. Most patients will feel well in that circumstance.

But some need a higher dose of levothyroxine to suppress serum TSH and then the serum-free T4 concentration will be elevated at around 24-28pmol/l.

This ‘exogenous subclinical hyperthyroidism’ is not dangerous as long as serum T3 is unequivocally normal – that is, serum total around T3 1.7nmol/l (reference range 1.0-2.2nmol/l).


Thanks Shaws, sorry yes I'm Hypo.

That's what I thought - as long as the FT3 is in range but that's when he said about subclinical and clinical hyper and totally lost me!

I will contact Louise for a copy, will definitely show him this. :)


Hi Denise, Once you are on thyroid hormone replacement, a low TSH does NOT make you hyper per se.

TSH (Thyroid Stimulating Hormone) is a pituitary hormone that stimulates the thyroid to make thyroid hormone. In a person not on any thyroid treatment, a low TSH coupled with a high FT3 means they are hyperthyroid.

In a person taking thyroid hormone replacement, the link between the thyroid and the pituitary is broken and the TSH drops by itself without any connection to the levels of FT4 and FT3. The TSH no-longer indicates thyroid status with any accuracy - this is why we are always saying that TSH should NOT be used to determine the dose.

If your endo wants a better picture of your thyroid status (hypo, euthyroid, hyper, etc) he should measure your frees. Your present TSH has nothing to do with being hyper - clinical or subclinical - and everything to do with you taking T3. If he reduces your T3 and ups your T4, your TSH may come up, but you will probably feel more symptoms.

Also, TSH is not necessary to your health. All it does is stimulate your thyroid. You don't need it for anything else. Therefore, if it doesn't exist once you are taking thyroid hormone orally, it is not a problem. It will not affect your health in any way. And you are not hyper unless your FT3 is way over range.

There have been so many studies done on this. You'd think a so-called 'hormone specialist' would know, wouldn't you! Pft!

Hugs, Grey

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Thanks Grey

As I said to Shaws above, I said about my FT3 & FT4 being well within range and that's when he said' oh yes but there's being hyperthyroid and then there's being sub-clinically hyper, at which point I was lost lol

He's saying that he doesn't want my TSH to go below 0.5. It was 0.07 at one point but now seems to be rising, so I'll see on the next test if it's risen further. All he's worried about is my heart and bones, which apparently all rests on my TSH! If their that worried why don't they do ALL the tests they should do, instead of my asking for them. Grrr

You would think they'd know about this stuff, it's driving me mad!!!!! I only want to feel well, not carry out crazy experiments on my body to prove a point or for the hell of it!!!

I suppose, I just wanted to understand what he meant by clinical/sub-clinical so he can't bamboozle me again. Also so I can get any written proof of this, which Shaws has pointed out to me :)

It makes sense to me that my symptoms returning and my TSH rising on the same meds is not a coincidence but of course it can't be that obvious.

Thanks again Grey for the great info as always :)


Yes, they do say that low TSH is dangerous for your bones and your heart, but I think they might have been daydreaming when that bit was explained to them in med school! lol

If you are not on any thyroid hormone, and your TSH is suppressed and your T3 is high, then you are hyper. Being hyper - i.e. having too much T3 - can cause heart and bone problems. But it has nothing to do with the TSH per se. You don't need a certain amount of TSH in order to preserve your heart and bones because TSH has nothing to do with heart and bones. It's the excess T3 that affects them. All the TSH does is stimulate the thyroid. But somehow these wonderful creatures that we call 'doctor' have got it all upside down and... Well, you get my drift. I do hope that the written proof that Shaws has given you sets him straight. It would be nice to know that at least one of them has got it the right way up!

Hugs, Grey


Haha That's what I thought Grey but for a second there, I thought the doc knew something I didn't! lol

Thank you :)


Nah, he was trying to blind you with science. lol Same with the clinical/sub-clinical hyperthyroidism. I doubt if he really knows what sub-clinical means. Or at least, it doesn't mean what he thinks it means.


I see. That eplains lot then. Many thanks for this reply.

POAs were less than 33. Is that significant?


If we could all be treated as this doctor did and doctors before blood tests (although blood tests can be helpful of course but not to the extent that the patient


This is how patients were/are treated by some doctors:-


Why did the endo say I have subclinical  hyperthyroidism then>


Hi Lucy, I really cannot say. I know nothing about your case, and you Don't seem to have posted your labs anywhere. Do you have a copy of your latest labs?


I suppose it all dépends on your definition of 'sub-clinical' hyperthyroidism.


It appears that the definition is a ow TSh in the presence of 'normal' range T3 and T4.

There are papers on Pubmed and Medscape that describe this condition and its treatment.


Well, I Don't know, that sounds crazy to me. If the TSH is low and the FT4 and FT3 are low normal, that's would be secondary hypo in my book.  


Sorry about typos. Should read low tsh.


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